Positive electrode material for lithium secondary battery, lithium secondary battery, and secondary battery module using lithium secondary battery

ABSTRACT

A lithium secondary battery of excellent high temperature cycle characteristic using, as a positive electrode material, a surface-covering lithium manganese composite oxide capable of stably suppressing the leaching of Mn even at high temperature and high voltage without lowering the electric conductivity, in which the positive electrode material for the lithium secondary battery is a lithium transition metal composite oxide having a hexagonal layered structure and represented by a compositional formula: LiMn x M 1-x O 2  (in which 0.3≦x≦0.6, M is one or more elements selected from the group consisting of Li, B, Mg, Al, Co, and Ni), or a lithium transition metal composite oxide having a cubic spinel structure and represented by a compositional formula: LiMn y N 1-y O 4  (in which 1.5≦y≦1.9, N is one or more elements selected from the group consisting of Li, Mg, Al, and Ni), and the lithium transition metal composite oxide has a metal fluoride and a lithium phosphate compound on the surface thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithium secondary battery.

2. Description of the Related Art

In recent years, lithium secondary batteries are generally used as powersources for small size equipment such as personal computers or portableequipment since they have high energy density. Further, application ofthe lithium secondary batteries has been investigated as power sourcesfor environment-friendly electric cars and hybrid cars, and stationarypower sources compensating for power fluctuation that will be caused bynatural phenomena by combining with renewable energy of electric powersuch as solar power generation or wind power generation. Low cost andlong life are particularly required in the field of large-scale lithiumbatteries.

At present, lithium cobaltate is predominant as the positive electrodematerial for the lithium secondary battery. However, lithium cobaltateis expensive since the yield of cobalt as the starting material issmall, which makes the cost reduction difficult. Further, when lithiumcobaltate is kept under a high voltage state, this raises a problem thatcobalt leaches out of a positive electrode material and the battery lifeis greatly shortened.

Therefore, with an aim of cost reduction and long operating life of thebattery, utilization of nickel, iron, manganese, etc. has been studiedas substitute metals for cobalt, but nickel involves a problem thatlithium nickelate remarkably lowers safety during overcharge or capacityduring cyclic operation. In contrast, iron recently attracts attentionas lithium iron phosphate having an orthorhombic olivine structure andis excellent in safety, but this material involves a problem that theelectric conductivity is low or the operation voltage is low.

On the other hand, lithium manganese composite oxide is excellent insafety during overcharge since the crystal structure is more stable incomparison with lithium cobaltate. Further, since the electricconductivity is almost 1 digit higher, lithium manganese composite oxideis advantageous in the life property. However, manganese leaches fromthe lithium manganese composite oxide into an electrolyte during hightemperature storage. As a result, leaching-out manganese clogs aseparator or forms a film layer on a negative electrode,disadvantageously leading to increase in battery resistance anddeterioration of battery characteristics.

Manganese leaches out of the lithium manganese composite oxide sincetrivalent Mn has Jahn-Teller effect (structure of lowered symmetricityis more stable). When trivalent Mn becomes instable in terms of energy,this produces more stable bivalent Mn and tetravalent Mn and bivalent Mnleaches as ions.

For example, Japanese Patent No. 3142522 describes that a portion of Mnsites in LiMn₂O₄ having a spinel structure is substituted by Li or atransition metal so as to decrease the ratio of trivalent Mn containedin a positive electrode material, thereby improving the cycle property.When a portion of Mn is substituted by tri- or smaller valent element,the mean valence of Mn contained in a positive electrode increases and,as a result, the ratio of trivalent Mn decreases. However, using elementsubstitution alone is not sufficient to suppress the leaching of Mn fromthe surface of the positive electrode material. Further, since the meanvalence of Mn increases, capacity is lowered.

To suppress leaching of Mn from the surface of the positive electrodematerial, the surface of the lithium manganese composite oxide iscovered with a metal oxide or a metal sulfide in Japanese Patent No.3944899, while the surface of the positive electrode material is coveredwith a fluoro compound in JP-A No. 2008-536285. However, under thecondition at high temperature and high voltage, a metal oxide or a metalsulfide of low standard generation enthalpy is instable. Therefore, thematerial is insufficient to suppress leaching of Mn from the surface ofthe positive electrode. Further, since the fluoride compound has noelectric conductivity, when the surface of the electrode is completelycovered, the electric conductivity is lowered, resulting in the batterycharacteristic deteriorating.

SUMMARY OF THE INVENTION

To address the above-described problems, the present invention intendsto provide a lithium secondary battery excellent in high temperaturecycle property by using, as a positive electrode material, asurface-covering lithium manganese composite oxide capable of stablysuppressing the leaching of Mn also at high temperature and high voltagewithout lowering the electric conductivity.

The positive electrode material for a lithium secondary battery of theinvention has a metal fluoride and a lithium phosphate compound on thesurface of a lithium transition metal composite oxide.

Further, the lithium secondary battery of the invention contains thepositive electrode material for the lithium secondary battery describedabove.

The lithium secondary battery of the invention can extend the lifeparticularly under a high temperature state.

DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Other objects and advantages of the invention will become apparent fromthe following description of embodiments with reference to theaccompanying drawings in which:

FIG. 1 is a cross sectional view of a 18650 type lithium ion secondarybattery according to the invention;

FIG. 2 is a view showing an X-ray diffraction pattern for a positiveelectrode material of the invention;

FIG. 3 is a graph showing XPS spectrum of the positive electrode of theinvention; and

FIG. 4 is a view schematically showing a secondary battery system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A positive electrode material for a lithium secondary battery, a lithiumsecondary battery, and a secondary battery module according to theinvention are to be descried.

The positive electrode material for the lithium secondary battery andthe lithium secondary battery according to the invention have a metalfluoride and a lithium phosphate compound on the surface of the lithiumtransition metal composite oxide containing at least Mn as a transitionmetal. In the lithium secondary battery of the invention, a positiveelectrode capable of occluding and releasing lithium and a negativeelectrode capable of occluding and releasing lithium are formed by wayof an electrolyte.

Further, the lithium transition metal composite oxide comprises: alithium transition metal composite oxide having a hexagonal layeredstructure and represented by a compositional formula: LiMn_(x)M_(1-x)O₂(in which 0.3≦x≦0.6, M is one or more elements selected from the groupconsisting of Li, B, Mg, Al, Co, and Ni), or a lithium transition metalcomposite oxide having a cubic spinel structure and represented by acompositional formula: LiMn_(y)N_(1-y)O₄ (in which 1.5≦y≦1.9, N is oneor more elements selected from the group consisting of Li, Mg, Al, andNi).

Further, the metal fluoride is preferably AF_(z) (in which 2.0≦z≦3.0,and A is a metal element between group 2 and group 13 and preferably oneor more members selected from the group consisting of AlF₃, NiF₂, andMgF₂. The content is preferably 0.1% by weight or more and 3.0% byweight or less of the lithium transition metal composite oxide.

Further, the lithium phosphate compound is preferably one or moremembers selected from the group consisting of Li₃PO₄, Li₄P₂O₇, andLiPO₃. The content is preferably 0.1% by weight or more and 3.0% byweight or less of the lithium transition metal composite oxide.

Further, in the lithium secondary battery of the invention, the capacityretention is 75% or more when put to 1000 cycle operation in a range of2.7 V or higher and 4.2 V or lower at a charge/discharge late of 0.5 Cin a atmosphere at 50° C.

Further, the secondary battery module of the invention has a pluralityof electrically connected batteries and a control device for managingand controlling the state of the plurality of batteries. The controldevice detects the inter-terminal voltage for the plurality ofbatteries. The plurality of batteries each comprises a laminate having apositive electrode, a negative electrode, and an electrolyte formed in abattery can. The positive electrode has a lithium transition metalcomposite oxide having a hexagonal layered structure and represented bya compositional formula: LiMn_(x)M_(1-x)O₂ (in which 0.3≦x≦0.6, M is oneor more elements selected from the group consisting of Li, B, Mg, Al,Co, and Ni), or a lithium transition metal composite oxide having acubic spinel structure and represented by a compositional formula:LiMn_(y)N_(1-y)O₄ (in which 1.5≦y≦1.9, N is one or more elementsselected from the group consisting of Li, Mg, Al, and Ni). Further thelithium transition metal oxide has a metal fluoride and a lithiumphosphate compound on the surface thereof.

Then, one of embodiments for practicing the invention is to be describedspecifically.

FIG. 1 shows a schematic cross sectional view of a lithium secondarybattery.

In the lithium secondary battery, a separator 3 intervenes between apositive electrode 1 and a negative electrode 2. The positive electrode1, the negative electrode 2, and the separator 3 are wound and sealedtogether with a non-aqueous electrolyte into a battery can 4 made ofstainless steel or aluminum. A positive electrode lead 7 is formed atthe positive electrode 1 and a negative electrode lead 5 is formed atthe negative electrode 2 respectively, from which electric current istaken out. An insulation sheet 9 is formed between the positiveelectrode 1 and the negative electrode lead 5, and between the negativeelectrode 2 and the positive electrode lead 7 respectively. A packing 8is formed between the battery can 4 in contact with the negativeelectrode lead 5 and a lid 6 in contact with the positive electrode lead7 for preventing leakage of the electrolyte and isolating the pluselectrode and the minus electrode.

The positive electrode 1 is formed by coating a current collectorcomprising aluminum or the like with a positive electrode mix. Thepositive electrode mix comprises an active material contributing toocclusion and release of lithium, a conductive material for improvingthe electric conductivity and a binder for ensuring intimate contactwith a current collector.

The negative electrode 2 is formed by coating the current collectorcomprising copper or the like with a negative electrode mix. Thenegative electrode mix has an active material, a conductive material, abinder, etc. For the active material of the negative electrode 2, metallithium, a carbon material, or a material capable of intercalatinglithium or forming a lithium compound can be used and the carbonmaterial is particularly preferred. The carbon material includesgraphites such as natural graphites and artificial graphites andamorphous carbon, for example, carbides of coal type coke and coal typepitch, and carbides of petroleum type coke and petroleum type pitch, andcarbides of pitch coke. The carbon materials described above appliedwith various surface treatments are preferred. The carbon materials maybe used not only alone but also as a combination of two or more of them.Further, materials capable of intercalating lithium or forming a lithiumcompound include metals such as aluminum, tin, silicon, indium, gallium,and magnesium, alloys containing these elements, and metal oxidescontaining tin, silicon, etc. Further, composite materials of themetals, alloys, or metal oxides and carbon materials such as graphitetype material or amorphous carbon as described above can also be sited.

As the active material for the positive electrode 1, a lithiumtransition metal composite oxide is used. As the transition metal, it ispreferred that at least inexpensive Mn is contained and a lithiummanganese composite oxide (hereinafter referred to as “composite oxide”)is used. Those having various crystal structures have been known as suchcomposite oxide, and it is preferred to use those having hexagonallayered structure and represented by the compositional formula:LiMn_(x)M_(1-x)O₂ (in which 0.3≦x≦0.6 and M is one or more elementsselected from the group consisting of Li, B, Mg, Al, Co, and Ni) andthose having a cubic spinel structure and represented by thecompositional formula: LiMn_(y)N_(1-y)O₄ (in which 1.5≦y≦1.9 and N isone or more elements selected from the group consisting of Li, Mg, Al,and Ni). In LiMn_(x)M_(1-x)O₂ and LiMn_(y)N_(1-y)O₄, diffusion path forLi are 2-dimensional and 3-dimensional respectively. Since orthorhombicolivine structure represented by LiFePO₄, as a representative example,has a 1-dimensional diffusion path for Li, the positive electrodematerial of the layered structure and the spinel structure have anadvantage that the Li electric conductivity is higher than that of thepositive electrode material having the olivine structure. However, ithas been known that in the positive electrode material of the layeredstructure and the spinel structure, Li diffusion paths are hindered bysite exchange of Li and Mn to lower the Li conductivity. For suppressingthe site exchange between Li and the transition metal, occupation ratioof Mn in the lithium diffusion paths can be lowered by substituting aportion of transition metal sites by dissimilar metals. As the elementused for substitution, those elements with lower valence number such astri or smaller valence are preferred for decreasing the ratio oftrivalent Mn. In the invention, the ratio of the trivalent Mn can bedecreased without lowering Li diffusion by using monovalent Li, bivalentMg or Ni, or trivalent B, Al, or Co for the positive electrode materialof the layered structure, and monovalent Li, bivalent Mg or Ni ortrivalent Al as the substituent element for the positive electrodematerial of the spinel structure.

The content x for Mn in the positive electrode material having thelayered structure is: 0.3≦x≦0.6. When x<0.3, contribution to the costreduction for the lithium secondary battery by the use of Mn isinsufficient. On the other hand, when 0.6<x, many impurities such asinert Mn₂O₃, Mn₃O₄, and Li₂MnO₃ not contributing to the battery reactionare formed to lower the battery capacity. It is preferably: 0.3≦x≦0.5.

The content y for Mn in the positive electrode material having thespinel structure is: 1.5≦y≦1.9. When y<1.5, the mean valence of Mn ishigh and the amount of Mn contributing to donation and acceptance of Liis decreased to lower the battery capacity. On the other hand, when1.9<y, Mn tends to be leached to possibly shorten the life time. It ispreferably: 1.7≦y≦1.88.

The amount of oxygen is defined as 2 in the layered structure and as 4in the spinel structure and it has been known that this may be somewhatdeviated from a stoichiometric composition depending on the bakingcondition. Accordingly, it is considered that deviation of the oxygenamount by about 5% of the defined amount does not depart from the gistof the invention.

To suppress the leaching of Mn from the surface of the positiveelectrode material during high temperature storage, it has been foundpreferable that a metal fluoride and a lithium phosphate compound arepresent on the surface of the composite oxide. The metal fluoride isrepresented by AF_(z) (in which 2.0≦z≦3.0, and A is a metal elementbetween group 2 and group 13), has higher standard enthalpy of formationcompared with a metal oxide or a metal sulfide, and can be presentstably even under severe conditions such as high temperature and highvoltage. Further, since the metal fluoride is present stably withrelation to hydrogen fluoride generated by decomposition of lithiumsalt, etc. in an electrolyte, the acid resistance can be improvedremarkably to suppress leaching of Mn. Since it is preferred that themetal fluoride is inexpensive and light in the weight, MgF₂, AlF₃, andNiF₂ are preferred.

It has been found preferred that the content of the metal fluoride is0.1% by weight or more and 3.0% by weight or less of the compositeoxide. The metal fluoride present on the surface of the composite oxidedecreases the area of contact between the composite oxide and theelectrolyte and suppresses the leaching of Mn due to active ingredientssuch as hydrogen fluoride contained in the electrolyte. Accordingly,when the content of the metal oxide is less than 0.1% by weight of thecomposite oxide, a role of decreasing the area of contact between thecomposite oxide and the electrolyte cannot be provided sufficiently. Onthe other hand, in a case when the content of the metal fluoride exceeds3.0% by weight, since the metal fluoride itself is an insulator, thisremarkably lowers the capacity. In this case, each weight of MgF₂, AlF₃,and NiF₂ per one mol is 62.3, 84.0, and 96.7 g, respectively. Since theweights of the metal fluorides described above are different with eachother, a more preferred range for the weight is also different. Each ofMgF₂ and AlF₃ is 0.2% by weight or more and 1.2% by weight or less, andNiF₂ is 0.3% by weight or more and 1.8% by weight or less of thecomposite oxide.

While the kind and the content of the metal fluoride are important forsuppressing leaching of Mn, the state of coverage is also one ofparameters indispensable for suppressing the leaching of Mn. The metalfluoride is preferably present in the form of covering 50% or more and99% or less of the surface of the composite oxide. This is because themetal fluoride itself is an insulator and the electric conductivity islowered when it completely covers the surface. Further, the thickness ofthe cover film is also preferably about 5 nm or more and 50 nm or less.When the thickness is less than 5 nm, cracking is caused due toexpansion and shrinkage of the positive electrode material duringcharge/discharge and the leaching of Mn can no more be suppressed. Onthe other hand, when it exceeds 50 nm, the electronic conductivity islowered abruptly.

Further, by applying a heat treatment after covering the composite oxideby the metal fluoride, a solid solution layer is formed at the boundarybetween the metal fluoride and the composite oxide. The solid solutionlayer is considered to have a structure in which the metal element inthe metal fluoride substitutes on Mn sites in the composite oxide, andcontributes to the stabilization of Mn in the composite oxide. Withoutheat treatment, intimate adhesion between the metal fluoride and thecomposite oxide is poor and the covering film comprising the metalfluoride is destroyed by the expansion and shrinkage of the positiveelectrode material during charge/discharge reaction to possiblyeliminate the effect of covering.

Further, it has been found that since the electric conductivity islowered when the composite oxide is covered with the metal fluoridealone, lowering of the electric conductivity can be suppressed bydistributing a lithium phosphate compound together with the metalfluoride. The lithium phosphate compound includes Li₃PO₄, Li₄P₂O₇, andLiPO₃ of high electric conductivity and LiFPO₄, LiMnPO₄, LiNiPO₄, andLiCoPO₄ capable of occluding and releasing lithium although theelectronic conductivity is low. In the invention, it is preferred thatthe lithium phosphate compound has high electric conductivity and hasLi₃PO₄, Li₄P₂O₇, or LiPO₃ together with the metal fluoride. Inparticular, Li₃PO₄ is superior to other compounds in the heat stabilityand the electric conductivity, and it is most suitable.

Further, distribution of the lithium phosphate compound is alsoimportant. For example, when it is present between the composite oxideand the metal fluoride, this is not preferred since the effect ofimproving the electric conductivity by the lithium phosphate compound issmall and, in addition, intimate adhesion between the composite oxideand the metal fluoride is lowered to decrease the effect of suppressingthe leaching of Mn by the metal fluoride. Lithium phosphate compound ispreferably present more on the metal fluoride or on the surface of thecomposite oxide not covered with the metal fluoride. When at leastone-half or more of the lithium phosphate compound to be contained isdistributed on the sites described above, it is possible tocompatibilize suppression for the leaching of Mn by the metal fluorideand the improvement in the electric conductivity due to the lithiumphosphate compound.

It has been found that the content of the lithium phosphate compound is0.1% by weight or more and 3.0% by weight or less of the compositeoxide. When the content of the lithium phosphate compound is less than0.1% by weight, lowering of the electric conductivity cannot becompensated. When the content is 3.0% by weight or more, the compound ispeeled from the composite oxide and present as a dissimilar material tolower the battery characteristic. More preferably, it is 0.2% by weightor more and 2.0% by weight or less.

To cause the metal fluoride and the lithium phosphate compound to bepresent on the surface of the composite oxide, a surface coveringtreatment is necessary. At first, three patterns may be considered asthe step of covering the surface of the composite oxide by the metalfluoride and the lithium phosphate compound, that is, in a state ofpowder, in a state of electrode or a state of operating as a battery.When covering is applied in a state of electrode, since the electrode isusually coated on both surfaces of a current collector, applying thecovering treatment on both surfaces of the current collector isnecessary. Furthermore, since the current collector foil at thenot-coated portion of the electrode should not be covered, this makesthe step complicate. On the other hand, when the covering is applied inthe state of operation as the battery, the metal fluoride and thelithium phosphate compound have to be added as additives in theelectrolyte. In this case, when the particle diameter of the additive islarger than the pore size of the separator, clogging in the separator iscaused to greatly deteriorate the battery characteristic. Further, whenthe coating film is formed electrochemically on the surface of thepositive electrode, making the application of the heat treatment isdifficult. This raises a problem that the surface covering film isdestroyed by expansion and shrinkage of the positive electrode materialdue to charge/discharge, thereby failing to obtain the effect ofcovering.

Accordingly, the surface covering treatment is preferably conducted inthe state of the powder. The method of the surface treatment on thepowder generally includes a solid phase method and a liquid phase methodand the liquid phase method is preferred. The advantage of the liquidphase method is that the surface of the composite oxide can be covereduniformly, the particle diameter of the covering material can becontrolled, the surface of the composite oxide may be less injuredphysically, etc.

In the present invention, two kinds of materials, that is, the metalfluoride and the lithium phosphate compound are present on the surfaceof the composite oxide.

It may not suffice that the metal fluoride and the lithium phosphatecompound are merely present. The coating state is important forcompatibilizing the suppression of the leaching of Mn from the surfaceof the positive electrode and the electric conductivity. The metalfluoride has a role of decreasing the area of contact between thepositive electrode material and the electrolyte and is preferablydistributed widely on the surface of the positive electrode. On theother hand, since the lithium phosphate compound has a role ofmaintaining the electric conductivity which is lowered by the metalfluoride, it is preferably present on the metal fluoride or on thesurface of the composite oxide not covered with the metal fluoride.

Accordingly, in the surface treatment step, the surface of the positiveelectrode is at first coated with the metal fluoride and then with thelithium phosphate compound thereon. Subsequently, the intimate adhesionbetween the positive electrode material and the coating film is improvedby the heat treatment. It has been found that by covering in this order,a firm film which is less destroyed even by expansion and shrinkage ofthe positive electrode material during charge/discharge can be formed.

To cover the surface of the positive electrode by the metal fluoride,the following procedures may also be adopted. At first, the surface ofthe positive electrode is covered by the metal oxide or the metalsulfide and maintained in a fluorine gas atmosphere to convert thecoating film on the surface to a metal fluoride. Then, after coveringthe lithium phosphate compound as described above, a heat treatment isapplied.

The positive electrode material, for the lithium secondary battery,having the metal fluoride and the lithium phosphate compound on thesurface of the lithium transition metal composite oxide may be usedalone, or two or more kinds of the positive electrode material and thecovering compound may be used in admixture while changing the coveringcondition. Further, it may be used in admixture with a not-coveredpositive electrode material or a positive electrode material having anorthorhombic olivine structure.

The lithium secondary battery of the invention has a charge retention of75% or more and, preferably, 80% or more when the battery is put to1,000 cycles of operation within a range of 2.7 V or higher and 4.2 V orlower at a charge/discharge rate of 0.5 C in a atmosphere at 50° C.

“Charge/discharge rate 1 C” means that 100% charge is completed in onehour when charge starts from a state where the battery is completelydischarged, and that 100% discharge is completed in one hour whendischarge starts from a state where the battery is completely charged.That is, this means that the charge or discharge rate is 100% per onehour. Accordingly, in a case where charge/discharge rate is 0.5 C, thecharge or discharge rate is 100% per 2 hours, that is, 100% charge ordischarge is completed in 2 hours.

Then, a manufacturing method in which the composite oxide is used as thepositive electrode material is to be described.

As the starting material for the positive electrode material, thefollowings can be used.

As the lithium compound, lithium hydroxide, lithium carbonate, lithiumnitrate, lithium acetate, lithium chloride, lithium sulfate, etc. can beused and lithium hydroxide and lithium carbonate are preferred.

As the manganese compound, manganese hydroxide, manganese carbonate,manganese nitrate, manganese acetate, manganese sulfate, manganeseoxide, etc. can be used, and manganese carbonate and manganese oxide arepreferred. The compound as the substitution element includes hydroxides,carbonates, nitrates, acetates, sulfites, oxides, etc.

The materials as the raw material are supplied as a powder of apredetermined compositional ratio, and this is pulverized and mixed by amechanical method using, for example, a ball mill. Pulverization andmixing may be conducted by using either dry or wet process. Then, theobtained powder is baked at 800° C. or higher and 1000° C. or lower,preferably, 850° C. or higher and 950° C. or lower. The atmosphere uponbaking is preferably an oxidative gas atmosphere such as oxygen or air.A mean secondary particle diameter of the powder obtained after bakingis preferably 3 μm or more and 30 μm or less. When the diameter is lessthan 3 μm, the specific surface area is excessively large therebyincreasing the area of contact between the electrolyte and the positiveelectrode material, and Mn tends to be leached. On the other hand, whenthe diameter exceeds 30 μm, the Li diffusion paths in the positiveelectrode material are made longer which is disadvantageous forocclusion and releasing of Li. More preferably, the diameter is 5 μm ormore and 25 μm or less.

The thus obtained positive electrode material powder is used and then asurface treatment is applied.

The surface treatment method by the liquid phase method is describedbelow.

A nitrate, an acetate, or a sulfate containing a metal element selectedfrom the group consisting of Mg, Al, and Ni is dissolved by apredetermined amount of water or an organic solvent. Further afluorine-containing compound is dissolved, separately, by using the samesolvent. As the fluorine-containing compound, ammonium fluoride ispreferred. Then, after mixing the two kinds of solutions, pH is adjustedsuch that the aqueous solution becomes weakly alkaline of pH of 8 ormore and 10 or less by using a pH controller. The pH controllerincludes, for example, ethanolamine, sodium hydroxide, and aqueousammonia. By forming such an weakly alkaline solution, reaction betweenthe metal source and the compound as the fluorine source is acceleratedand a metal fluoride is precipitated. The positive electrode materialdescribed above is mixed in the solution thus prepared, and a metalfluoride is deposited on the surface. Then, after adding water or anorganic solvent in which the phosphate is dissolved, the solvent isevaporated from the solution. The solvent is preferably evaporated bystirring under heating or spray drying. Finally, the obtained powder issubjected to a heating treatment at 300° C. or higher and 700° C. orlower, preferably, 400° C. or higher and 600° C. or lower. By theheating treatment, precipitates deposited on the surface of the positiveelectrode particle are reacted and intimate adhesion can be providedbetween the metal fluoride and the positive electrode material. The timefor the heating treatment is one hour or more and 20 hours or less and,preferably, 3 hours or more and 8 hours or less.

Alternatively, the metal fluoride can also be used as a cover withoutadding the fluoro compound by keeping the same in a fluorine gasatmosphere. As the fluorine gas, a nitrogen trifluoride gas ispreferred.

(Confirmation of Crystal Structure)

The crystal structure of the manufactured positive electrode materialwas measured for a diffraction profile by a radiation source CuKα usingan automatic X-ray diffractometer (RINT-Ultima III, manufactured byRigaku Corp., hereinafter simply referred to as XRD). The crystalstructure was confirmed based on the peak angles of the obtaineddiffraction profile.

(Method of Measuring Mean Particle Diameter)

The mean particle diameter of the positive electrode material wasmeasured as below by the laser diffraction/scattering method using alaser diffraction/scattering particle diameter distribution analyzer(LA-920 manufactured by Horiba Seisakusho Co.). At first, 0.2% by weightof sodium hexamethaphosphate mixed as a dispersant to purified water wasused, and materials were charged. For suppressing the coagulation of thematerials, after applying supersonic waves for 5 minutes, the mediandiameter (particle diameter for particles at a relative amount ofparticles of 50%) was measured and defined as a mean particle diameter.

(Method of Measuring Weight Ratio of Elements)

The weight ratio of metal elements used for the surface treatment andthe weight ratio of Mn dissolved in the electrolyte were measured by ahigh frequency inductively coupled plasma atomic emission (hereinaftersimply referred to as ICP) spectrometer (P-4000, manufactured by HitachiLtd.). At first, 5 g of a positive electrode material, and 2 mL ofnitric acid or 5 mL of electrolyte were charged into 45 mL of ionexchange water placed in a beaker, and stirred it by a stirrer for 30minutes. After leaving it for 5 minutes, a filtrate filtered throughfilter paper was sprayed together with an argon gas in a high frequencyatmosphere, and the light intensity inherent in each of the excitedelement was measured to calculate the weight ratio of elements.

(Confirmation of Covering Compound)

For the bonding state of the surface coating compound, spectrum for eachof elements was measured by a radiation AlKα using an X-rayphotoelectronic (hereinafter simply referred to as XPS) spectrometer(AXIS-HS, manufactured by Shimadzu/KRATOS Co). For the coating compound,the spectrum for the metal element contained in the compound wasmeasured and the peak position was compared with that of the StandardReference Database 20 Version 3.5 for NIST, to decide the compoundspecies.

An example of the method of manufacturing a lithium secondary battery isas shown below.

A slurry is prepared by mixing the positive electrode material togetherwith a conductive material of a carbon material powder and a binder suchas polyvinylidene fluoride. The mixing ratio of the conductive materialto the positive electrode material is preferably 3% by weight or moreand 10% by weight or less. The mixing ratio of the binder to thepositive electrode material is preferably 2% by weight or more and 10%or less by weight.

In this case, for uniformly dispersing the positive electrode materialin the slurry, it is preferably kneaded sufficiently by using a kneader.

Both surfaces of an aluminum foil are coated with the obtained slurrywith a thickness of 15 μm or more and 25 μm or less, for example, by aroll transfer machine. After both surface coating, an electrode plate ofthe positive electrode plate 1 is formed by press drying. The thicknessfor the portion of the mix formed by mixing the positive electrodematerial, the conductive material, and the binder is preferably 200 μmor more and 250 μm or less.

As with the positive electrode, the negative electrode material is mixedwith the binder, used as a coat and pressed to form an electrode. Inthis case, the thickness of the electrode mix is preferably 20 μm ormore and 70 μm or less. In a case of the negative electrode, a copperfoil of a thickness of 7 μm or more and 20 μm or less is used as acurrent collector. The mixing ratio in the coating is preferably, forexample, 90:10 as the weight ratio between the negative electrodematerial and the binder.

The covered and pressed positive electrode and negative electrode arecut each into a predetermined length, and a tab for drawing out acurrent is formed by spot welding or supersonic welding. The tabcomprises a current collector in a rectangular shape and a metal foil ofthe same material, and is disposed for taking out the current from theelectrode. A separator comprising a finely porous film, for example, ofpolyethylene (PE) or polypropylene (PP) is sandwiched and stackedbetween the positive electrode and the negative electrode each having atab, and they are wound into a cylindrical shape to form an electrodegroup and contained in a cylindrical container. Alternatively, abag-shaped separator in which an electrode is contained may be stackedsuccessively and contained in a square container. The material for thecontainer is preferably stainless steel or aluminum. After containingthe electrode group in the battery can, an electrolyte is injectedtherein and sealed tightly.

For the electrolyte, it is preferred to use those formed by dissolvinglithium hexafluoro phosphate (LiPF₆), lithium tetrafluoro borate(LiBF₄), lithium perchlorate (LiClO₄), etc. as an electrolyte into asolvent such as diethyl carbonate (DEC), dimethyl carbonate (DMC),ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate(VC), methyl acetate (MA), ethyl methyl carbonate (EMC), methyl propylcarbonate (MPC), etc. The concentration of the electrolyte is preferably0.7 M or more and 1.5 M or less. The electrolyte is poured and thebattery container was closed tightly to complete a battery.

Examples are to be described more specifically but the invention is notrestricted to the examples.

Example 1 Manufacture of Positive Electrode Material

In Example 1, lithium carbonate, triamanganese tetraoxide, cobaltdioxide, and nickel oxide were used as the starting material formanufacturing the positive electrode material, they were weighed suchthat Li:Mn:Co:Ni was 1.02:0.34:0.5:0.14 at the raw material ratio, andpulverized admixed in a wet process by a pulverizer. After drying, thepowder was placed in a high purity alumina container and provisionallybaked in an atmospheric air at 600° C. for 12 hours in order to improvethe sinterability. Then, the powder was again placed in the high purityalumina container and baked under the conditions of keeping for 12 hoursin an atmospheric air at 900° C., air cooled and then crushed andclassified. FIG. 2 shows an X-ray diffraction profile for the obtainedpositive electrode material. The obtained peak was compared withInternational Center for Diffraction Data Card (PDF-2) to confirm thatthis was in a hexagonal layered structure. Accordingly, the compositionof the positive electrode material isLiMn_(0.34)(Li_(0.02)Co_(0.5)Ni_(0.14))O₂. Further, when the grain sizedistribution of the positive electrode material was measured, the meanparticle diameter was 6 μm.

The surface treatment step is to be described.

100 mL of ion exchange water in which 0.66 g of ammonium fluoride wasdissolved was added to 100 mL of ion exchange water in which 2.3 g ofaluminum nitrate was dissolved, to prepare a mixed solution. Then,lithium hydroxide was added as a pH controller to the mixed solution tocontrol pH of the mixed solution to 10.0. Then, 100 g of the positiveelectrode material was charged and, finally, 300 mL of ion exchangewater in which 0.78 g of hydrogen diammonium phosphate was dissolved wasadded and stirred at a normal temperature for one hour. Then, thesolution was dried by a spray drier and the obtained powder was placedin a highly pure alumina container and heated at 600° C. for 5 hours.

FIG. 3 shows spectra for A12p and P2p obtained by XPS analysis of thepositive electrode material after the surface treatment. A12p had a peakat 76.3 eV, and this agreed with AlF₃ from the data base. Further P2phad a peak at 133.6 eV and this agreed with Li₃PO₄ from the data base.From the result, it was found that AlF₃ and Li₃PO₄ were present on theuppermost surface of the positive electrode material.

The positive electrode material was put to ICP analysis and it was foundthat AlF₃ was 0.5% by weight and a Li₃PO₄ was 0.5% by weight of thepositive electrode material, based on the weight ratio of Al and P toMn.

(Manufacture of Positive Electrode)

A positive electrode was manufactured by using the obtained positiveelectrode material. The positive electrode material, the carbonaceousconductive material, and binder dissolved previously intoN-methyl-2-pirrolidone (NMP) as the solvent were mixed at a ratio of85:10:5 respectively expressed by mass %, and an aluminum currentcollector foil was coated uniformly with mixed slurry with a thicknessof 20 μm. Then, it was dried at 120° C., and compression molded by apress such that the electrode density was 2.7 g/cm³. After compressionmolding, it was punched out into a disc-shape of 15 mm diameter by usinga punching tool to manufacture a positive electrode.

(Manufacture of Test Battery)

By using the positive electrode described above, and using metal lithiumas the negative electrode and a mixed solvent of ethyl carbonate anddimethyl carbonate as a liquid electrolyte to manufacture a testbattery. The liquid electrolyte uses 1.0 mol of LiPF₆ as an electrolyte.

Evaluation for the leaching amount of Mn is to be described.

The leaching amount of Mn from the positive electrode was evaluated bythe following procedures. With a test battery, after charging until 4.3V was reached with constant current/constant voltage at a charge rate of0.5 C, it was discharged until a desired amount of discharged voltagewas reached with a constant current at a discharge rate of 0.5 C. Afterrepeating the operations three cycles, the battery was charged until 4.3V was reached with a constant current/constant voltage at a charge rateof 0.5 C. Then, the test battery was disassembled, and the positiveelectrode was taken out therefrom. The charged electrode and 5 cc of aliquid electrolyte in which 1 mol/L of LiPF₆ was dissolved in an organicsolvent solution formed by mixing EC and MEC at volume ratio of 1:2 wereplaced in a container made of a fluoro resin (PFA) and closed tightly ina globe box in an argon atmosphere. The container was taken out of theglobe box, placed in a thermostat bath at 80° C. and left for 1 week.After one week, the container was taken out of the thermostat bath, and5 cc of the electrolyte was taken out in the globe box in an argonatmosphere. Mn dissolved in the taken out electrolyte was measuredquantitatively by using an ICP apparatus.

The calculated leaching amount of Mn was 7 ppm.

Table 1 shows the characteristic of the positive electrode materialmanufactured in Example 1.

TABLE 1 Amount Leaching Positive Amount of amount electrodeLiMn_(x)M_(2-x)O_(y) of AF_(z) Li₃PO₄ of Mn material x y M AF_(z) (wt %)(wt %) (ppm) Example 1 0.31 2 Li, Co, Ni AlF₃ 0.5 0.5 7

Manufacture of a 18650 (18 mm diameter×650 mm height) type battery is tobe described.

A 18650 type battery was manufactured by using the obtained positiveelectrode material. At first, the surface treated positive electrodematerial, the conductive material of carbon material powder and a binderof PVdF were mixed at the weight ratio of 90:5:5 and an appropriateamount of NMP was added to prepare a slurry.

The prepared slurry was stirred by a planetary mixer for 3 hours toconduct kneading.

Then, both surfaces of an aluminum foil of 20 μm thickness were coatedwith the kneaded slurry by using a coating machine of a roll transfermachine. This was pressed by a roll press machine such that the mixdensity was 2.70 g/cm³, to obtain a positive electrode.

By using graphite as the negative electrode active material, carbonblack as the conductive material, and PVdF as the binder, they weremixed at the weight ratio of 92:2:6 and stirred by a slurry mixer for 30minutes to conduct kneading.

Both surfaces of a copper foil of 10 μm thickness were coated with thekneaded slurry by using a coating machine and, after drying, pressed bya roll press, to obtain a negative electrode.

The positive electrode and the negative electrode were cut each into apredetermined size, and a current collector tab was disposed bysupersonic welding at a slurry not-coated portion.

A porous polyethylene film was sandwiched between the positive electrodeand the negative electrode and, after winding into a cylindrical shape,they were inserted into a 18650 type battery.

After connecting the current collector tab and the lid of the batterycan, the lid of the battery can and the battery can were welded by laserwelding to tightly seal the battery.

Finally, a non-aqueous liquid electrolyte was poured from a pore portformed into the battery can to obtain a 18650 type battery.

Evaluation for the rate characteristic is to be described.

The rate characteristic of the manufactured 18650 type battery wasevaluated by the following procedures. At first, the battery was chargeduntil 4.2 V was reached with constant current/constant voltage at acharge rate of 0.2 C. After interval of one hour reoperation recess, thebattery was discharged until the discharged amount was reached 2.5 Vwith a constant current at a discharge rate of current of 0.2 C or moreand 10 C or less respectively. The discharge capacity upon discharge at10 C to the discharge capacity upon discharge at 0.2 C was defined as arate ratio (%). Table 2 shows a result.

Evaluation for the cycle characteristic is to be described.

The cycle characteristic of the manufactured 18650 type battery wasevaluated by the following procedures. The battery was charged until acharge terminal voltage was reached 4.2 V with constant current whileflowing a current of 0.5 C and, after interval of one hour operationrecess, the battery was discharged until the discharged amount wasreached 2.7 V with constant current of the same current value. Theoperations were repeated for 1,000 cycles and the capacity retention at1000 cycle/1 cycle was calculated. The test atmosphere temperature wasset at 50° C. Table 2 shows the result.

TABLE 2 Positive electrode Rate ratio Capacity retention material (%)(%) Example 1 92 85

Example 2

In this example, boron oxide was added as the raw material and the rawmaterials were weighed such that Li:Mn:Co:Ni:B was1.02:0.3:0.3:0.14:0.24 at raw material ratio, and the positive electrodematerial was manufactured in the same manner as in Example 1. Thecrystal structure in this example was a hexagonal layered structure andhad a composition of LiMn_(0.3)(Li_(0.02)Co_(0.3)Ni_(0.14)B_(0.24))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 4.6 g of aluminum nitride and 1.3 g of ammonium fluoride. As aresult of XPS analysis of the positive electrode material, presence ofAlF₃ and Li₃PO₄ could be confirmed on the uppermost surface, and fromthe result of ICP analysis, it was found that AlF₃ was 1.0% by weightand Li₃PO₄ was 0.5% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 9 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 2.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresults is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example2 shows high performance.

Example 3

In this example, aluminum oxide was used instead of cobalt dioxide asthe raw material and the raw materials were weighed such thatLi:Mn:Ni:Al was 1.02:0.5:0.2:0.27 at raw material ratio, and thepositive electrode material was manufactured in the same manner as inExample 1. The crystal structure in this example was a hexagonal layeredstructure and the composition wasLiMn_(0.5)(Li_(0.02)Ni_(0.2)Al_(0.27))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 0.7 g of magnesium nitrate instead of aluminum nitrate and 0.26g of ammonium fluoride and 0.31 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 0.2% by weightand Li₃PO₄ was 0.2% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 12 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 3.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example3 shows high performance.

Example 4

In this example, aluminum oxide and boron oxide were used instead ofcobalt dioxide as the raw material and the raw materials were weighedsuch that Li:Mn:Ni:Al:B was 1.02:0.3:0.1:0.27:0.2 at raw material ratio,and the positive electrode material was manufactured in the same manneras in Example 1. The crystal structure in this example was a hexagonallayered structure and the composition was LiMn_(0.3)(Li_(0.02)Ni_(0.1)Al_(0.27):B_(0.2))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 0.64 g of nickel nitrate instead of aluminum nitrate and 1.3 gof ammonium fluoride and 3.1 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofNiF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that NiF₂ was 0.5% by weightand Li₃PO₄ was 2.0% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 4 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 4

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example4 shows high performance.

Example 5

In this example, aluminum oxide was added as the raw material and theraw materials were weighed such that Li:Mn:Co:Ni:Al was1.05:0.4:0.3:0.15:0.1 at raw material ratio, and the positive electrodematerial was manufactured in the same manner as in Example 1. Thecrystal structure in this example was a hexagonal layered structure andhad a composition of LiMn_(0.4 (Li) _(0.05)Co_(0.3)Ni_(0.15)Al_(0.1))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 1.8 g of magnesium nitrate instead of aluminum nitrate and 1.6g of hydrogen diammonium phosphate. As a result of XPS analysis of thepositive electrode material, presence of MgF₂ and Li₃PO₄ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that MgF₂ was 0.5% by weight and Li₃PO₄ was 1.0% by weightof the positive electrode material. In this example, the leaching amountof Mn was 1 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 5.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example5 shows high performance.

Example 6

In this example, magnesium oxide was added as the raw material and theraw materials were weighed such that Li:Mn:Co:Ni:Mg was1.02:0.4:0.35:0.20:0.03 at raw material ratio, and the positiveelectrode material was manufactured in the same manner as in Example 1.The crystal structure in this example was a hexagonal layered structureand had a composition ofLiMn_(0.4)(Li_(0.02)Co_(0.35)Ni_(0.2)Mg_(0.03))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 1.6 g of hydrogen diammonium phosphate. As a result of XPSanalysis of the positive electrode material, presence of AlF₃ and Li₃PO₄could be confirmed at the outermost surface, and from the result of ICPanalysis, it was found that AlF₃ was 0.5% by weight and Li₃PO₄ was 1.0%by weight of the positive electrode material. In this example, theleaching amount of Mn was 5 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 6.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example6 shows high performance.

Example 7

In this example, magnesium oxide was used instead of cobalt dioxide asthe raw material and the raw materials were weighed such thatLi:Mn:Ni:Mg was 1.02:0.6:0.2:0.18 at the raw material ratio, and thepositive electrode material was manufactured in the same manner as inExample 1. The crystal structure in this example was a hexagonal layeredstructure and the composition wasLiMn_(0.6)(Li_(0.02)Ni_(0.2)Mg_(0.18))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 1.4 g of aluminum nitrate and 0.4 g of ammonium fluoride and0.31 g of hydrogen diammonium phosphate. As a result of XPS analysis ofthe positive electrode material, presence of AlF₃ and Li₃PO₄ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that AlF₃ was 0.3% by weight and Li₃PO₄ was 0.2% by weightof the positive electrode material. In this example, the leaching amountof Mn was 5 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 7.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example7 shows high performance.

Example 8

In this example, lithium carbonate, trimanganese tetraoxide, andmagnesium oxide were used as the raw material and the raw materials wereweighed such that Li:Mn:Mg was 1.08:1.88:0.04 at the raw material ratio,and the positive electrode material was manufactured in the same manneras in Example 1. The crystal structure in this example was cubic spinelstructure and the composition was LiMn_(1.88)(Li_(0.08)Mg_(0.04))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 4.6 g of aluminum nitrate, and 1.3 g of ammonium fluoride and2.3 g of hydrogen diammonium phosphate. As a result of XPS analysis ofthe positive electrode material, presence of AlF₃ and Li₃PO₄ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that AlF₃ was 1.0% by weight and Li₃PO₄ was 1.5% by weightof the positive electrode material. In this example, the leaching amountof Mn was 21 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 8.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example8 shows high performance.

Example 9

In this example, lithium carbonate, trimanganese tetraoxide, and nickeloxide were used as the raw material and the raw materials were weighedsuch that Li:Mn:Ni was 1.04:1.9:0.06 at the raw material ratio, and thepositive electrode material was manufactured in the same manner as inExample 1. The crystal structure in this example was a cubic spinelstructure and the composition was LiMn_(1.9)(Li_(0.04)Ni_(0.06))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 14 g of magnesium nitrate instead of aluminum nitrate and 4 gof ammonium fluoride and 3.1 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 3.0% by weightand Li₃PO₄ was 2.0% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 10 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 9.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example9 shows high performance.

Example 10

In this example, lithium carbonate, trimanganese tetraoxide and aluminumoxide were used as the raw material and the raw materials were weighedsuch that Li:Mn:Al was 1.08:1.7:0.22 at the raw material ratio, and thepositive electrode material was manufactured in the same manner as inExample 1. The crystal structure in this example was a cubic spinelstructure and the composition was LiMn_(1.7)(Li_(0.08)Al_(0.22))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 2.5 g of nickel nitrate instead of aluminum nitrate and 0.73 gof ammonium fluoride and 3.1 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofNiF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that NiF₂ was 2.0% by weightand Li₃PO₄ was 2.0% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 14 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 10.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example10 shows high performance.

Example 11

In this example, lithium carbonate, trimanganese tetraoxide, nickeloxide, and aluminum oxide were used as the raw material and the rawmaterials were weighed such that Li:Mn:Ni:Al was 1.02:1.5:0.2:0.28 atthe raw material ratio, and the positive electrode material wasmanufactured in the same manner as in Example 1. The crystal structurein this example was a cubic spinel structure and the composition wasLiMn_(1.5)(Li_(0.02)Ni_(0.2)Al_(0.28))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 3.5 g of magnesium nitrate instead of aluminum nitrate and 1.3g of ammonium fluoride and 1.6 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 1.0% by weightand Li₃PO₄ was 1.0% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 7 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 11.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example11 shows high performance.

Example 12

In this example, lithium carbonate, trimanganese tetraoxide, magnesiumoxide and aluminum oxide were used as the raw materials and the rawmaterials were weighed such that Li:Mn:Mg:Al was 1.04:1.82:0.04:0.1 atthe raw material ratio, and the positive electrode material wasmanufactured in the same manner as in Example 1. The crystal structurein this example was a cubic spinel structure and the composition wasLiMn_(1.82)(Li_(0.04)Mg_(0.04)Al_(0.1))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 0.64 g of nickel nitrate instead of aluminum nitrate and 0.33 gof ammonium fluoride and 1.6 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofNiF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that NiF₂ was 0.5% by weightand Li₃PO₄ was 1.0% by weight of the positive electrode material. Inthis example, the leaching amount of Mn was 18 ppm by weight.

Table 3 shows the characteristic of the positive electrode materialmanufactured in Example 12.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 4.

It can be seen that also the positive electrode manufactured in Example12 shows high performance.

TABLE 3 Leaching Positive Amount Amount amount electrodeLiMn_(x)M_(2-x)O_(y) of of of Mn material x y M AF_(z) AF_(z) Li₃PO₄(ppm) Example 2 0.30 2 Li, Co, Ni, B AlF₃ 1.0 0.5 9 Example 3 0.50 2 Li,Al, Ni MgF₂ 0.2 0.2 12 Example 4 0.42 2 Li, Ni, Al, B NiF₂ 0.5 2.0 4Example 5 0.40 2 Li, Al, Co, Ni MgF₂ 0.5 1.0 1 Example 6 0.40 2 Li, Mg,Co, Ni AlF₃ 0.5 1.0 5 Example 7 0.60 2 Li, Ni, Mg AlF₃ 0.3 0.2 5 Example8 1.88 4 Li, Mg AlF₃ 1.0 1.5 21 Example 9 1.90 4 Li, Ni MgF₂ 3.0 2.0 10Example 10 1.70 4 Li, Al NiF₂ 2.0 2.0 14 Example 11 1.50 4 Li, Al, NiMgF₂ 1.0 1.0 7 Example 12 1.82 4 Li, Mg, Al NiF₂ 0.5 1.0 18

TABLE 4 Positive electrode Rate ratio Capacity retention material (%)(%) Example 2 87 90 Example 3 86 82 Example 4 94 88 Example 5 91 93Example 6 92 90 Example 7 85 83 Example 8 90 80 Example 9 87 82 Example10 88 77 Example 11 85 86 Example 12 87 75

Comparative Example 1

In this comparative example, in comparison with Example 1, tricobalttetraoxide as the raw material was removed and the raw materials wereweighed such that Li:Mn:Ni was 1.02:0.8:0.18 at raw material ratio andthe positive electrode material was manufactured in the same manner asin Example 1. The crystal structure in this example was a hexagonallayered structure and had a composition ofLiMn_(0.8)(Li_(0.02)Ni_(0.18))O₂.

Then, a surface treatment was applied in the same manner as in Example 1by using 1.8 g of magnesium nitrate instead of aluminum nitrate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 0.5% by weightand Li₃PO₄ was 0.5% by weight of the positive electrode material. Inthis comparative example, the leaching amount of Mn was 65 ppm byweight. This is because the Mn ratio in the positive electrode materialwas high and the mean valence number of Mn was excessively low.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 1.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 1 was inferior in both of the rateratio and the capacity retention compared with that manufactured in theexamples.

TABLE 5 Amount Leaching Positive Amount of amount electrodeLiMn_(x)M_(2-x)O_(y) of AF_(z) Li₃PO₄ of Mn material x y M AF_(z) (wt %)(wt %) (ppm) Comp. 0.80 2 Li, Ni MgF₂ 0.5 0.5 65 Example 1 Comp. 0.31 2Li, Co, Ni — — 0.5 308 Example 2 Comp. 0.30 2 Li, Co, Ni, B MgF₂ 0.050.1 35 Example 3 Comp. 0.30 2 Li, Co, Ni, B AlF₃ 9.0 3.0 0 Example 4Comp. 0.31 2 Li, Co, Ni, AlF₃ 2.0 — 10 Example 5 Comp. 0.30 2 Li, Co,Ni, B MgF₂ 1.0 0.05 10 Example 6 Comp. 0.30 2 Li, Co, Ni, B MgF₂ 1.0 8.09 Example 7 Comp. 1.88 4 Li, Mg NiF₂ 1.0 1.5 161 Example 8 Comp. 1.96 4Li, Mg AlF₃ 1.0 1.0 117 Example 9

TABLE 6 Positive electrode Rate ratio Capacity retention material (%)(%) Comp. Example 1 73 56 Comp. Example 2 86 39 Comp. Example 3 89 68Comp. Example 4 11 65 Comp. Example 5 32 78 Comp. Example 6 50 81 Comp.Example 7 88 60 Comp. Example 8 66 46 Comp. Example 9 63 55

Comparative Example 2

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 1.

Then, aluminum nitrate and ammonium fluoride were removed and a surfacetreatment was applied in the same manner as in Example 1. As a result ofXPS analysis of the positive electrode material, presence of Li₃PO₄ atthe outermost surface could be confirmed, and from the result of ICPanalysis, it was found that Li₃PO₄ was 0.5% by weight of the positiveelectrode material. In this comparative example, the leaching amount ofMn was 308 ppm by weight. This is because the effect of decreasing thearea of contact between the electrolyte and the positive electrodematerial caused by the metal fluoride was not obtained.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 2.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 2 was inferior in the capacityretention compared with that manufactured in the Examples.

Comparative Example 3

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 2.

Then, a surface treatment was applied in the same manner as in Example 1by using 0.23 g of magnesium nitrate instead of aluminum nitrate and0.07 g of ammonium fluoride and 0.04 g of hydrogen diammonium phosphate.As a result of XPS analysis of the positive electrode material, presenceof MgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 0.05% by weightand Li₃PO₄ was 0.1% by weight of the positive electrode material. Inthis comparative example, the leaching amount of Mn was 35 ppm byweight. This is because the amount of the metal fluoride was small andthe positive electrode surface could not be covered sufficiently.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 3.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 3 was inferior in the capacityretention compared with those manufactured in the Examples.

Comparative Example 4

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 2.

Then, a surface treatment was applied in the same manner as in Example 1by using 41 g of aluminum nitrate, 12 g of ammonium fluoride, and 4.7 gof hydrogen diammonium phosphate. As a result of XPS analysis of thepositive electrode material, presence of AlF₃ and Li₃PO₄ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that AlF₃ was 9.0% by weight and Li₃PO₄ was 3.0% by weightof the positive electrode material. In this comparative example, theleaching amount of Mn was at the detection limit or less (less than 0.5ppm).

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 4.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 4 was inferior both in the rateratio and the capacity retention compared with those manufactured in theexamples. This is because the metal fluoride as an insulator completelycovered the surface of the positive electrode to lower the conductivity.

Comparative Example 5

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 1.

Then, hydrogen diammonium phosphate was removed and a surface treatmentwas applied in the same manner as in Example 1 by using 9.2 g ofaluminum nitrate and 2.6 g of ammonium fluoride. As a result of XPSanalysis of the positive electrode material, presence of AlF₃ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that AlF₃ was 2.0% by weight of the positive electrodematerial. In this comparative example, the leaching amount of Mn was 10ppm by weight.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 5.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 5 was greatly inferior in the rateratio compared with those manufactured in the examples. This is becausethe electrode was covered only with the metal fluoride as an insulator.

Comparative Example 6

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 2.

Then, a surface treatment was applied in the same manner as in Example 1by using 3.6 g of magnesium nitrate instead of aluminum nitrate, and 1.3g of ammonium fluoride and 0.08 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 1.0% by weightand Li₃PO₄ was 0.05% by weight of the positive electrode material. Inthis comparative example, the leaching amount of Mn was 10 ppm byweight.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 6.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 6 was inferior in the rate ratiocompared with those manufactured in the examples. This is because theamount of the lithium phosphate compound was small, which wasinsufficient for the conductivity.

Comparative Example 7

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 2.

Then, a surface treatment was applied in the same manner as in Example 1by using 3.6 g of magnesium nitrate instead of aluminum nitrate, and 1.3g of ammonium fluoride and 12 g of hydrogen diammonium phosphate. As aresult of XPS analysis of the positive electrode material, presence ofMgF₂ and Li₃PO₄ could be confirmed at the outermost surface, and fromthe result of ICP analysis, it was found that MgF₂ was 1.0% by weightand Li₃PO₄ was 8.0% by weight of the positive electrode material. Inthis comparative example, the leaching amount of Mn was 9 ppm by weight.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 7.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 7 was inferior in the capacityretention compared with those manufactured in the examples. This isbecause the amount of the lithium phosphate compound was excessivelylarge.

Comparative Example 8

In this comparative example, a positive electrode material wasmanufactured in the same manner as in Example 8.

Then, in the surface treatment step, 100 g of a positive electrodematerial was charged into 300 mL of ion exchange water in which 2.3 g ofhydrogen diammonium phosphate was dissolved. After lithium hydroxide wasadded to 200 mL of ion exchange water in which 1.2 g of nickel nitrateand 0.38 g of ammonium fluoride were dissolved to prepare a mixedsolution at pH 10, it was added to a solution containing the positiveelectrode material and stirred at a normal temperature for one hour.After that, a surface treatment was applied in the same manner as inExample 1. As a result of XPS analysis of the positive electrodematerial, presence of NiF₂ and Li₃PO₄ could be confirmed at theoutermost surface, and from the result of ICP analysis, it was foundthat NiF₂ was 1.0% by weight and Li₃PO₄ was 1.5% by weight of thepositive electrode material. In this comparative example, the leachingamount of Mn was 161 ppm by weight. This is because the positiveelectrode surface could not be covered sufficiently by the metalfluoride. This state was considered to be formed that since the coatingorder was changed, the lithium phosphate compound was present on thesurface of the positive electrode and the metal fluoride was coatedfurther thereover.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 8.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 8 was inferior both in the rateratio and capacity retention compared with those manufactured in theexamples.

Comparative Example 9

In this example, lithium carbonate, trimanganese tetraoxide, andmagnesium oxide were used as the raw material and the raw materials wereweighed such that Li:Mn:Mg was 1.02:1.96:0.02 at the raw material ratio,and the positive electrode material was manufactured in the same manneras in Example 1. The crystal structure in this example was a cubicspinel structure and the composition wasLiMn_(1.96)(Li_(0.02)Mg_(0.02))O₄.

Then, a surface treatment was applied in the same manner as in Example 1by using 4.6 g of aluminum nitrate, 1.3 g of ammonium fluoride, and 1.6g of hydrogen diammonium phosphate. As a result of XPS analysis of thepositive electrode material, presence of AlF₃ and Li₃PO₄ could beconfirmed at the outermost surface, and from the result of ICP analysis,it was found that AlF₃ was 1.0% by weight and Li₃PO₄ was 1.0% by weightof the positive electrode material. In this comparative example, theleaching amount of Mn was 117 ppm by weight. This is because the amountof Mn contained in the positive electrode material having the cubicspinel structure is excessively large and the ratio of trivalentmanganese was increased.

Table 5 shows the characteristic of the positive electrode materialmanufactured in Comparative Example 9.

A 18650 type battery was manufactured in the same manner as in Example 1and the energy density and the capacity retention were evaluated. Theresult is shown in Table 6.

From Table 5 and Table 6, it was found that the positive electrodemanufactured in Comparative Example 9 was inferior both in the rateratio and capacity retention compared with those manufactured in theexamples.

The embodiment of the invention can provide a lithium secondary batterycapable of suppressing leaching of Mn and excellent in the rate ratioand the cycle life by providing a metal fluoride compound and a lithiumphosphate compound on the surface of lithium transition metal compositeoxide.

FIG. 4 shows an outline of a secondary battery system on which lithiumsecondary batteries manufactured in the embodiments are mounted.

A plurality of numbers, for example, four or more and eight or lessLithium secondary batteries 10 are connected in series to form a groupof lithium secondary batteries. Then, a plurality of groups of thelithium secondary batteries is further provided to constitute asecondary battery module.

Cell controllers 11 are formed corresponding to the groups of thelithium secondary batteries as described above and control the lithiumsecondary batteries 10. The cell controllers 11 monitor overcharge oroverdischarge of the lithium secondary batteries 10 or monitor theresidual capacity of the lithium secondary batteries.

A battery controller 12 provides a signal to the cell controller 11, forexample, by using communication means and obtains a signal from the cellcontroller 11, for example, by using communication means.

The battery controller 12 manages the input and output of power to andfrom the cell controller 11.

The battery controller 12 provides a signal, for example, to the inputsection 111 of the first cell controller 11. Such a signal istransmitted in series from the output section 112 of the cell controller11 to the input section 111 of other cell controller 11. Such a signalis given from the output section 112 of the final cell controller 11 tothe battery controller 12.

Thus, the battery controller 12 can monitor the cell controller 11.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1. A positive electrode material for a lithium ion secondary battery,wherein the positive electrode material includes a lithium transitionmetal composite oxide containing at least Manganese as a transitionmetal, and a metal fluoride and a lithium phosphate compound are on asurface of the lithium transition metal composite oxide.
 2. The positiveelectrode material according to claim 1, wherein the lithium transitionmetal composite oxide is represented by LiMn_(x)M_(1-x)O₂, in which0.3≦x≦0.6, and M is one or more elements selected from the groupconsisting of Li, B, Mg, Al, Co, and Ni, or represented byLiMn_(y)N_(1-y)O₄, in which 1.5≦y≦1.9, and N is one or more elementsselected from the group consisting of Li, Mg, Al, and Ni.
 3. Thepositive electrode material according to claim 2, wherein the lithiumtransition metal composite oxide represented by LiMn_(x)M_(1-x)O₂ has ahexagonal layered structure.
 4. The positive electrode materialaccording to claim 2, wherein the lithium transition metal compositeoxide represented by LiMn_(y)N_(1-y)O₄ has a cubic spinel structure. 5.The positive electrode material according to claim 1, wherein the metalfluoride is represented AF_(z), in which A is a metal element, and2.0≦z≦3.0.
 6. The positive electrode material according to claim 5,wherein the metal element A is a metal selected from metal elementsbetween group 2 and group
 13. 7. The positive electrode materialaccording to claim 5, wherein the metal fluoride is one or morecompounds selected from the group consisting of AlF₃, NiF₂, and MgF₂. 8.The positive electrode material according to claim 1, wherein thelithium phosphate compound is one or more compounds selected from thegroup consisting of Li₃PO₄, Li₄P₂O₇, and LiPO₃.
 9. The positiveelectrode material according to claim 1, wherein the content of themetal fluoride is 0.1% by weight or more and 3.0% by weight or less ofthe lithium transition metal composite oxide.
 10. The positive electrodematerial according to claim 1, wherein the content of the lithiumphosphate compound is 0.1% by weight or more and 3.0% by weight or lessof the lithium transition metal composite oxide.
 11. A lithium ionsecondary battery, comprising a positive electrode, a negativeelectrode, a separator located between said positive electrode and saidnegative electrode, and an electrolyte, wherein the positive electrodehas a lithium transition metal oxide, and a metal fluoride and a lithiumphosphate compound are on a surface of the lithium transition metaloxide, wherein the lithium transition metal oxide is represented byLiMn_(x)M_(1-x)O₂ in which 0.3≦x≦0.6, and M is one or more elementsselected from the group consisting of Li, B, Mg, Al, Co, and Ni, orLiMn_(y)N_(1-y)O₄ in which 1.5≦y≦1.9, and N is one or more elementsselected from the group consisting of Li, Mg, Al, and Ni.
 12. Thelithium ion secondary battery according to claim 11, wherein the metalfluoride is AF_(z) in which 2.0≦z≦3.0, and A is a metal element betweengroup 2 and group
 13. 13. The lithium ion secondary battery according toclaim 12, wherein the metal fluoride is one or more members selectedfrom the group consisting of AlF₃, NiF₂, and MgF₂.
 14. The lithium ionsecondary battery according to claim 11, wherein the lithium phosphatecompound is one or more members selected from the group consisting ofLi₃PO₄, Li₄P₂O₇, and LiPO₃.
 15. The lithium ion secondary batteryaccording to claim 11, wherein the content of the metal fluoride is 0.1%by weight or more and 3.0% by weight or less of the lithium transitionmetal composite oxide.
 16. The lithium ion secondary battery accordingto claim 11, wherein the content of the lithium phosphate compound is0.1% by weight or more and 3.0% by weight or less of the lithiumtransition metal composite oxide.
 17. The lithium ion secondary batteryaccording to claim 11, wherein the capacity retention is 75% or morewhen the battery is put through 1000 cycles in a range of 2.7 V orhigher and 4.2 V or lower at a charge/discharge rate of 0.5 C in anatmosphere at 50° C.
 18. A secondary battery module comprising: aplurality of batteries electrically connected; and a control device formanaging and controlling the state of the plurality of batteries whichdetects the inter-terminal voltage for the plurality of batteries;wherein each of the plurality of batteries comprises a positiveelectrode, a negative electrode, an electrolyte, and a battery can, inwhich the positive electrode and the negative electrode are layered,wherein the positive electrode comprises a lithium transition metaloxide, and a metal fluoride and a lithium phosphate compound on thesurface of the lithium transition metal oxide, and wherein the lithiumtransition metal oxide is represented by LiMn_(x)M_(1-x)O₂ in which0.3≦x≦0.6, and M is one or more elements selected from the groupconsisting of Li, B, Mg, Al, Co, and Ni, or LiMn_(y)N_(1-y)O₄ in which1.5≦y≦1.9, and N is one or more elements selected from the groupconsisting of Li, Mg, Al, and Ni.